Hi honetzeya !
This is really, really strange, I'm afraid that I will need more information to be able to help you.
Was the file moved out of the app "Documents" directory? (The documents directory is the forger directory under "On my iPad/iPhone" in the Files app on your device.
Did the app crash while saving over the file? (theoretically this shouldn't happen as the app saves to a temp file and then moves it over and overwrites if necessary, to avoid stuff like this)
How much free disk space does your device have?
Which device and iOS/iPadOS version are you using?
Which version of the app?